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MrHomeScientist
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Transparent Sodium?
Today I came across this extremely interesting video by Thoisoi2 on an observation he made of sodium in water:
<iframe sandbox width="560" height="315" src="https://www.youtube.com/embed/DJGVZNth68k" frameborder="0" allowfullscreen></iframe>
After placing sodium metal on a wet filter paper floating in a bowl of water, the sodium doesn't explode right away - instead it stops burning
completely and goes <I>transparent</I>. Really crazy, and I've never noticed this before. I will definitely try this at some point.
I think he covers all the points I was going to make here, in his narration already. My first hypothesis is that this is a blob of NaOH, or
concentrated NaOH solution, floating on a cushion of gas (hydrogen from the sodium reaction, or water vapor from the heat of dissolution
<I>ala</I> the leidenfrost effect). I think it still explodes in the end from the NaOH falling off the cushion and rapidly boiling the
water around it. But that's awfully fast for the whole blob of Na to get converted completely to NaOH. I think the clip at 4:00 supports the
hypothesis that it is a solution, as you can see a lot of bubbling in the droplet that (I think) wouldn't happen if it were some sort of transparent
metal instead.
What's everyone think? Very cool video if nothing else.
[Edited on 2-27-2015 by MrHomeScientist]
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deltaH
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The Leidenfrost effect is often touted as an explanation, but has anyone ever dropped a drop/blob of molten sodium hydroxide from a spatula into some
water and seen if it indeed behaves similarly and gives a similar pop explosion at the end?
It's been mentioned on another thread somewhere that there is now increasing evidence that the sodium explosion is, in fact, a 'coulombic explosion'
resulting from the build-up of unbalanced charges. Perhaps the transparent bead phase is molten sodium hydroxide with a slight excess of Na+ causing a
pop.
If testing with ordinary molten sodium hydroxide does not give similar behaviour (which I doubt it would), then I think there's the beginning of some
support for such a charge imbalance hypothesis.
[Edited on 27-2-2015 by deltaH]
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Zyklon-A
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Thunderf00t did a lot of research on this and there's is indeed much evidence that's its a coulombic explosion. He also has a lot of footage of the
transparent sodium.
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deltaH
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I don't like this term 'transparent sodium' which I think is just sensationalism. Even if it is charge imbalanced, is is still probably almost
entirely sodium hydroxide or a hydrate thereof, not just sodium.
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MrHomeScientist
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I agree that molten NaOH would almost certainly sink if dropped in water, as its density is greater (as mentioned in the video). Perhaps the sodium
reaction generates the cushion of gas the droplet can float on, which a blob dropped in water would not have in place. It still seems extremely quick
to react the chunk of sodium completely into transparent molten NaOH. I think a blob of primarily NaOH with some dissolved sodium is a good candidate.
Edit:
Possibly obscure reference: I wonder what this guy would think about "transparent sodium"?
[Edited on 2-27-2015 by MrHomeScientist]
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deltaH
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MrHomeScientist, I remember that 
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blogfast25
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Quote: Originally posted by deltaH  | | I don't like this term 'transparent sodium' which I think is just sensationalism. Even if it is charge imbalanced, is is still probably almost
entirely sodium hydroxide or a hydrate thereof, not just sodium. |
Of course. No need to look any further.
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morganbw
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Nothing to add, (too dumb to offer insight), but the video was pretty thought provoking.
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aga
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For the stupid amongst us (ok, just me then) can anyone say exactly Why sodium cannot exist in any state in which it is transparent ?
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phlogiston
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On the contrary, seems like a pretty good question to me.
I was going to argue that metals are reflective/not transparent to light because they are conductive.
Light, being an oscillating electromagnetic field, should not pass through electrically conductive materials.
However, I just realised a solution of a salt by that mechanism should appear reflective as well, and it obviously doesn't. Perhaps it has to do with
the number and mobility of charge carriers being much higher in metals?
[Edited on 28-2-2015 by phlogiston]
-----
"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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aga
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I guess the key would be how photons travel, and how they interact with matrices of matter.
Research time !
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blogfast25
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| Quote: Originally posted by aga | | For the stupid amongst us (ok, just me then) can anyone say exactly Why sodium cannot exist in any state in which it is transparent ?
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According to the paper cited in the video it can be transparent in specific conditions.
At RT Na isn't transparent because the conduction electrons also reflect photons (light).
My guess is that this is molten sodium oxide. Heat from the initial reaction with water and combustion of the evolved hydrogen sets the sodium on
fire. The filter paper limits access to water, causing the sodium oxide to stay 'intact'. Only later does it get to react almost explosively with
water.
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aga
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Conduction electrons ?
Please elaborate.
Photon interacts with some electron(s) and gets absorbed/repelled/ejected in a way that it retains it's speed, yet it's trajectory is altered.
Edit:
As Work is done, i.e. the trajectory is altered, then Energy must be consumed, somewhere ...
[Edited on 28-2-2015 by aga]
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j_sum1
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This is intriguing if only because the old classic of sodium and water has had its mechanism challenged twice in the last few months. The thing we
thought we understood is now shown to be mechanistically more complex than imagined.
I agree, the most likely candidate for the transparent substance is molten Na2O. Fascinating to see it in this form.
The next question that arises (for me anyway) is, if this is indeed Na2O or NaOH, then by what mechanism does it explode? We have learned that the
explosion of Na is from coulombic repulsion. But I can't see that a molten salt would behave in the same way. I am going to have to try this.
As an aside, metals do transmit light if thin enough. I have some gold leaf that appears blue when you hold it up to the light.
As another aside, I have seldom seen the characteristic explosion of sodium on water. This is because I am usually using very small pieces when I do
this experiment. Less than half a gram and explosions are rare. The video specifies a "medium-sized piece". I guess the observations are dependent
on the size of the piece as well as other factors.
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Molecular Manipulations
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Blogfast, you sure it's sodium oxide? Melting point 1,132 °C, seems unlikely but at that temperature the Leidenfrost effect would
certainly occur, but at that temperature it would certainly be visibly bright red hot at least, although it would probably appear yellow due to
sodium's spectrum.
Perhaps there's another reason why it doesn't seem to be glowing.
If it was molten sodium oxide, could the explosion be because of the temps required for the Leidenfrost effect to keep it above the water, lessen
enough and it sinks, instantly vaporizing a lot of water? I think not. Coulombic explosion seems more probable, like the blob is not molten sodium
oxide but mostly sodium ions, perhaps a little oxide but not much.
-The manipulator
We are all here on earth to help others; what on earth the others are here for I don't know. -W. H. Auden
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m1tanker78
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| Quote: Originally posted by j_sum1 | This is intriguing if only because the old classic of sodium and water has had its mechanism challenged twice in the last few months. The thing we
thought we understood is now shown to be mechanistically more complex than imagined.
I agree, the most likely candidate for the transparent substance is molten Na2O. Fascinating to see it in this form.
The next question that arises (for me anyway) is, if this is indeed Na2O or NaOH, then by what mechanism does it explode? We have learned that the
explosion of Na is from coulombic repulsion. But I can't see that a molten salt would behave in the same way. I am going to have to try this.
As an aside, metals do transmit light if thin enough. I have some gold leaf that appears blue when you hold it up to the light.
As another aside, I have seldom seen the characteristic explosion of sodium on water. This is because I am usually using very small pieces when I do
this experiment. Less than half a gram and explosions are rare. The video specifies a "medium-sized piece". I guess the observations are dependent
on the size of the piece as well as other factors. |
I third this assertion. Back when I did a lot of experiments with sodium, I was also puzzled by this. This can be somewhat unreliably reproduced by
placing a piece of sodium in a dish with just enough water to float the molten sodium. I've always thought that the water became saturated with base
and slowed the reaction enough that the sodium could burn (in air) faster than it reacts with the water. The 'explosion' ensues when the glass bead
cools enough that it can contact the (relatively) cool lye solution.
So what happens if you drop a piece of sodium in a saturated NaOH solution??
Chemical CURIOSITY KILLED THE CATalyst.
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j_sum1
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Good points on temp glow etc MM.
I'm still not convinced on coulombic explosion if it is a non-metal at this stage. However, it looks the same as normal Na. It could be the same
mechanism. But that's going to require another rethink on what happens with sodium.
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Molecular Manipulations
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It makes more sense to me if the coulombic explosion takes place with a transparent substance. The lusterous, reflective sodium comes from only the
outer valance electron, once removed it becomes a colorless, non-reflective ion. It seems likely that ionized sodium, be itself would be colorless. I
just can't figure out what takes it so long to explode? Without something holding it together they would fly apart as soon as they're ionized, not
wait until most of them are ionized and then explode. So what's holding them together?
-The manipulator
We are all here on earth to help others; what on earth the others are here for I don't know. -W. H. Auden
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blogfast25
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Where did I say I was sure? It wouldn't have to molten sodium oxide either, come to think of it.
Coulombic explosion would be very superficial.
It's certainly intriguing, assuming it's not a hoax of course. And no, before y'll start getting myopic, I'm not saying it is, just that the
possibility should not be dismissed a priori. Weirder science hoaxes have been committed.
[Edited on 28-2-2015 by blogfast25]
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blogfast25
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Work out the mol fraction water in a saturated NaOH solution. That should put things into perspective.
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Molecular Manipulations
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I'm sure sodium would also react with pure sodium hydroxide to make sodium oxide and isolate hydrogen.
What do you mean by the "Coulombic explosion would be very superficial"?
My question is why does it take so long to explode? It appears not to be very superficial, else it would probably be more steady. Unless nothing
happens for a few seconds and the a lot of the sodium suddenly gets ionized in milliseconds?
[Edited on 28-2-2015 by Molecular Manipulations]
-The manipulator
We are all here on earth to help others; what on earth the others are here for I don't know. -W. H. Auden
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deltaH
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| Quote: Originally posted by Molecular Manipulations | I'm sure sodium would also react with pure sodium hydroxide to make sodium oxide and isolate hydrogen.
What do you mean by the "Coulombic explosion would be very superficial"?
My question is why does it take so long to explode? It appears not to be very superficial, else it would probably be more steady. Unless nothing
happens for a few seconds and the a lot of the sodium suddenly gets ionized in milliseconds?
[Edited on 28-2-2015 by Molecular Manipulations] |
Key to the coulomb explosion hypothesis is probably sodium's tendency to form electrides (solvated electrons). I presume the electrons diffuse out of
the drop and that the drop accumulates net Na[+].
My hypothetical explanation as to what then causes the delay is this:
Water has a very strong dielectric constant and would immediately pack around the 'naked' sodium ions so that their dipoles partially cancel out that
field. In effect, they decrease the field strength at a certain distance away from the Na+ that would otherwise have been there.
Water also strongly hydrogen bonds with itself with the net result that the cohesion between water molecules is unusually strong.
But as the charge builds up and more and more water shield Na+, an internal strain between the water molecules also start to build up and at some
point, the forces start to exceed water's ability to hold itself together.
At this point, just as in a solid, fracturing occurs, i.e. it starts out as a small breaking apart, but this seeds new 'tears' and quickly everything
goes flying apart from the stored potential energy of the coulombic strain.
******
Oh, some more speculative points:
The drop being liquid means that the unbalanced Na+ can diffuse around and would probably make their way to the surface of the drop, just as charges
on an insulator accumulate on the surface, so the 'strain' I was previously talking about could be nothing else than surface strain.
It pops when the strain caused by coulombic repulsion (partially shielded by water) exceeds the surface strain of the solution.
The amount of unbalanced sodium cations must surely be quite small or the forces and stored potential energy would be enormous and a much larger
explosion would have ensued.
[Edited on 28-2-2015 by deltaH]
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deltaH
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The naughty in me wonders how one could carry this out so as to favour the accumulation of a very large amount of strain and unbalanced charge,
trapped in a solid matrix like ice, for example, and not just on its surface.
Charge explosive
[sciencemadness=ON] Mill a slurry of ice and sodium in liquid nitrogen for a long time. Allow to warm up slowly... at some point BOOM!
Perhaps this can be done in a mortar and pestle by first pouring in some liquid nitrogen to cool down the M&P wearing face shield and gloves, then
to a decent pool of liquid nitrogen, add a tiny piece of ice and a tiny piece of sodium, mill under liquid nitrogen until very fine, place blast
shield in place, step back and wait for remaining liquid nitrogen to boil off and everything to heat up, make awesome video  [sciencemadness=OFF]
[Edited on 28-2-2015 by deltaH]
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blogfast25
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This phenomenon works (if we're to believe the video) if contact between the sodium and water is quite small (hence the filter paper).
Even at 50 w% NaOH the mole fraction of water is nearly 70 %, plenty of water to react with the sodium.
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m1tanker78
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Fair enough blogfast. Let me unpack my question. What purpose does the filter paper serve?
Chemical CURIOSITY KILLED THE CATalyst.
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